Polyamide 5x industrial yarn, preparation method therefor and use thereof

ABSTRACT

Disclosed in the present invention is a polyamide 5X industrial yarn. The polyamide 5X industrial yarn has a heat-resistant break strength retention rate of 90% or more after being treated at 180° C. for 4 hrs; a heat-resistant break strength retention rate of 90% or more after being treated at 230° C. for 30 mins; and a dry heat shrinkage of 8.0% or less. The polyamide 5X industrial yarn is widely used in the fields of sewing threads, tire cords, air bag yarns, release cloth, krama, canvas, safety belts, ropes, fishing nets, industrial filter cloth, conveyor belts, parachutes, tents, bags and suitcases.

TECHNICAL FIELD

The present invention relates to the technical field of polyamidematerials, and provides a polyamide 5X industrial yarn, a process forproducing the same and use thereof.

BACKGROUND ART

Industrial yarns can be produced by two processes: one process is adirect melt spinning process, and the other is an indirect chip spinningprocess by solid phase tackifying. Nowadays, a part of polyamide 66 andpolyethylene terephthalate sometimes has been produced by the directmelt spinning process. However, polyamide 6 can not be produced by thedirect melt-spinning process now because the polymer contains 8-10 wt %of monomers which need to be removed through a monomer removal process.

Dacron and Chinlon industrial yarns have the properties like highstrength, low elongation, good dimensional stability, and beingfatigue-resistant and aging-resistant. Therefore, they are widely usedin the fields of tire cords, canvas, conveyor belts, air bags,parachutes, ropes, safety belts, industrial filter cloth, tents, or thelike. Various application fields impose relatively high requirements onthe heat resistance of industrial yarn materials. At present, this ismainly achieved by a method of blending with a heat stabilizermasterbatch added. However, heat stabilizer masterbatches are expensive.Moreover, spinning manufacturers need to be equipped with an onlinemasterbatch device during spinning, which increases equipmentinvestment. In addition, there is also a need to address thecompatibility between the heat stabilizer masterbatch and the basematerial. If the masterbatch is not uniformly added, filaments breakduring spinning, which will reduce the production yield of theindustrial yarns and even affect the mechanical properties of thefibers.

CN 110055602A discloses a high-strength polyamide 56 industrial yarn anda process for producing the same. Conventional polyamide 56 chips areused for spinning, the polyamide 56 chips are not subjected to a heatresistance modification, and the produced industrial yarn has poor heatresistance and cannot be used in fields requiring high heat resistance,such as sewing threads, tire cords, airbag yarns, release cloth, kramaand the like. A high-speed winding process is adopted, wherein thewinding speed is greater than 4000 m/min. Since the winding speed ishigh, the residence times of the fibers on different hot rollers arerelatively short, that is, the high-temperature setting time of thefibers is shortened. Furthermore, by employing a process with a lowdrawing ratio, fibers are produced which have a low crystallinity, a loworientation degree, a low strength and a poor dimensional stability.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a polyamide 5Xindustrial yarn with both excellent heat resistance and mechanicalproperties. The polyamide 5X industrial yarn has a heat-resistant breakstrength retention rate of 90% or more after being treated at 180° C.for 4 hrs; a heat-resistant break strength retention rate of 90% or moreafter being treated at 230° C. for 30 mins; and/or a dry heat shrinkageof 8.0% or less. The polyamide 5X comprises any one of polyamide 56,polyamide 510, polyamide 512, polyamide 513 or polyamide 514. Preferenceis given to polyamide 56 or polyamide 510.

According to the present invention, the quality of polyamide 5X,especially polyamide 56 resin, is optimized by adjusting its viscosity,oligomer content, molecular weight and molecular weight distribution,moisture content. Secondly, the spinning process of the polyamide 5Xindustrial yarn is optimized, the crystallinity and orientation degreethereof are improved, the setting temperature and winding overfeed ratioare increased, the subsequent stress relaxation is reduced. In this way,the present invention provides a polyamide 56 industrial yarn withexcellent mechanical properties and dimensional stability which has abreak strength of 6.5 cN/dtex or more; a filament breakage of 2 times orless every 24 hrs, a production yield of 90% or more; a shrinkage inboiling water of 8.0% or less; a fineness of 100-3,500 dtex; anelongation at break of 26% or less; a crystallinity of 70% or more;and/or an orientation degree of 80% or more.

During the spinning process of polyamide fibers, it is necessary tocontrol the moisture content of the resins, which is generally requiredto be within the range of equilibrium moisture content. If the moisturecontent of the resin is too low during spinning, a melt tackifyingreaction occurs during melting, the amino content decreases, and thefluidity of the melt deteriorates, which is unfavorable for subsequentdrawing and causes filament breakage and low strength of fibers. If themoisture content is too high, a melt degradation reaction occurs duringmelting, the amino content increases, which tends to cause filamentbreakage and eventually leads to a reduced production yield. If themoisture content of polyamide 56 resin is controlled within the range of300-800 ppm during spinning, the oil-free yarn of the polyamide 56industrial yarn has a relative viscosity of 2.7-4.5, the absolute valueof the difference between the relative viscosity of the oil-free yarnand the relative viscosity of its original resin is 0.12 or less; theoil-free yarn has an amino content of 20-50 mmol/kg, the absolute valueof the difference between the amino content of the oil-free yarn and theamino content of its original resin is 5 or less. By reducing thefluctuation ranges in terms of the viscosity and the amino content ofthe oil-free yarn, the melt uniformity of the polyamide 56 is improved,the filament breakage is decreased, the spinnability can be improved,and the production yield of the polyamide 56 industrial yarn prepared is90% or more.

A second object of the present invention is to provide a process forproducing polyamide 5X industrial yarn, especially polyamide 56industrial yarn.

A third object of the present invention is to provide a use of thepolyamide 5X industrial yarn, especially polyamide 56 industrial yarn,in the fields of sewing threads, tire cords, air bag yarns, releasecloth, krama, canvas, safety belts, ropes, fishing nets, industrialfilter cloth, conveyor belts, parachutes, tents, bags and suitcases.

In order to achieve the above objects, the present invention providesthe following solutions:

[Polyamide 5X Industrial Yarn]

Taking polyamide 56 industrial yarn as an example, the content of copperions in the polyamide 56 industrial yarn according to the presentinvention is 10-1,000 ppm, preferably 30-500 ppm, and more preferably50-200 ppm; the polyamide 56 industrial yarn has a heat-resistant breakstrength retention rate of 90% or more, preferably 94% or more, and morepreferably 98% or more after being treated at 180° C. for 4 hrs; and/ora heat-resistant break strength retention rate of 90% or more,preferably 93% or more, and more preferably 96% or more after beingtreated at 230° C. for 30 mins; and/or the polyamide 56 industrial yarnhas a dry heat shrinkage of 8.0% or less, preferably 6.0% or less, andmore preferably 4.0% or less.

The polyamide 56 industrial yarn comprises a heat stabilizer;preferably, the heat stabilizer comprises any one of copper acetate,potassium iodide, copper chloride, cuprous iodide, copper oxide, cuprousoxide, or combination thereof; preferably, the heat stabilizer is addedin an amount of 10-2,800 ppm, and preferably 10-2,500 ppm, based on thetotal weight of the production raw materials.

Preferably, the heat stabilizer is a composition of copper acetate andpotassium iodide, wherein the molar ratio of copper acetate to potassiumiodide is 1:1-15, preferably 1:2-10, and more preferably 1:6-8, whereinpreferably copper acetate is added in an amount of 100-500 ppm, andpotassium iodide is added in an amount of 500-2,500 ppm.

The polyamide 56 industrial yarn has a break strength of 6.5 cN/dtex ormore, preferably 7.0 cN/dtex or more, and more preferably 8.0 cN/dtex ormore.

The oil-free yarn of the polyamide 56 industrial yarn has a relativeviscosity of 2.7-4.5, and the absolute value of the difference betweenthe relative viscosity of the oil-free yarn and the relative viscosityof its original resin is 0.12 or less, preferably 0.10 or less, and morepreferably 0.08 or less.

The oil-free yarn of the polyamide 56 industrial yarn has an aminocontent of 20-50 mmol/kg; and the absolute value of the differencebetween the amino content of the oil-free yarn and the amino content ofits original resin is 5 or less, preferably 3 or less, and morepreferably 2 or less.

The filament of the polyamide 56 industrial yarn breaks 2 times or lessevery 24 hrs, preferably 1 time or less every 24 hrs, and morepreferably 0 time every 24 hrs; and the production yield of thepolyamide 56 industrial yarn is 90% or more, preferably 93% or more, andmore preferably 96% or more.

The polyamide 56 industrial yarn has a shrinkage in boiling water of8.0% or less, preferably 7.0% or less, and more preferably 6.0% or less;and/or, the polyamide 56 industrial yarn has a fineness of 100-3,500dtex, preferably 200-2,500 dtex, and more preferably 300-1,800dtex;and/or, the polyamide 56 industrial yarn has an elongation at break of26% or less, and preferably 22% or less; and/or, the polyamide 56industrial yarn has a crystallinity of 70% or more, preferably 72% ormore, and more preferably 74% or more; and/or, the polyamide 56industrial yarn has an orientation degree of 80% or more, preferably 82%or more, and more preferably 84% or more.

Raw materials for producing the polyamide 56 industrial yarn at leastcomprise 1,5-pentane diamine and adipic acid; or a polyamide 56 obtainedby polymerizing 1,5-pentane diamine and adipic acid as monomers.

The 1,5-pentane diamine is prepared from bio-based raw materials by afermentation process or an enzymatic conversion process. Preferably, the1,5-pentane diamine is prepared from bio-based raw materials by afermentation process or an enzymatic conversion process. For example,the process for producing 1,5-pentane diamine as disclosed inCN109536542A is employed.

[Process for Producing Polyamide 5X Industrial Yarn]

Taking polyamide 56 industrial yarn as an example, the process comprisesthe following steps:

wherein the polyamide 56 industrial yarn can be prepared by twoprocesses, namely direct melt spinning process or chip spinning process;

(1) polymerizing 1,5-pentane diamine and adipic acid to obtain ahigh-viscosity polyamide 56 melt, conveying the melt to a spinning beamby a melt booster pump, and spinning directly; or using polyamide 56chip to spin, that is, firstly preparing a low-viscosity polyamide 56resin, then obtaining a high-viscosity polyamide 56 resin by solid phasetackifying, and heating the high-viscosity polyamide 56 resin into amolten state so as to form a polyamide 5X melt for spinning;

wherein in the solid phase tackifying, the viscosity is increased bydrying the low-viscosity polyamide 56 resin at a high temperature;preferably, the solid phase tackifying is performed at a temperature of120-180° C., preferably 150-160° C.; the drying time is 10-50 hrs, andpreferably 15-30 hrs; in the solid phase tackifying, moisture is removedby drying at a high temperature, and the polycondensation reactioncontinues to obtain a high-viscosity resin;

(2) drawing the polyamide 56 melt to form an as-spun yarn; and

(3) processing the as-spun yarn to obtain the polyamide 56 industrialyarn.

Wherein a heat stabilizer is added during the polymerization of1,5-pentane diamine and adipic acid in Step (1), or injected online inthe form of a heat stabilizer masterbatch before cutting the polymermelt into pellets, or blended in the form of a heat stabilizermasterbatch during the spinning.

If the polyamide 5X industrial yarn is a polyamide 510 industrial yarn,1,5-pentane diamine and sebacic acid may be polymerized.

In some embodiments of the present invention, the content of copper ionsin the heat stabilizer masterbatch is 0.5-10 wt %, preferably 0.8-5 wt%, and more preferably 1.2-3 wt %.

In some embodiments of the present invention, the heat stabilizermasterbatch is added in an amount of 0.3-5.0 wt %, preferably 0.5-3.0 wt%, and more preferably 0.8-2.0 wt %.

In some embodiments of the present invention, the base material for theheat stabilizer masterbatch is any one of polyamide 6, polyamide 56,polyamide 66, polyamide 510, polyamide 610, polybutylene terephthalate,or combination thereof; preferably polyamide 6, polyamide 56 and/orpolyamide 510; and more preferably polyamide 6 and/or polyamide 56.

In some embodiments of the present invention, the process for producingthe heat stabilizer masterbatch comprises the following steps:

(1) drying the base material under vacuum or in an inert gas andgrinding it into powders;

(2) mixing the powders obtained in Step (1) with a heat stabilizer andother additive(s), and pelletizing the mixture. Specifically, atwin-screw melt extrusion can be used for pelletization. Preferably, theprocessing temperature of each zone of the twin-screw extruder is180-285° C., the screw rotation speed is 25-350 r/min, the vacuum degreeis −0.1 MPa or less, and the filter screen is in the range of 80-200mesh. Preferably, the base material is polyamide 56, the processingtemperature of each zone of the twin-screw extruder is 260-275° C., thescrew rotation speed is 50-350 r/min, the vacuum degree is −0.1 MPa orless, and the filter screen is in the range of 100-150 mesh. The heatstabilizer is added in an amount of 0.5-20 wt %, based on the basematerial.

In some embodiments of the present invention, the heat stabilizer is acomposition of copper acetate and potassium iodide, wherein the molarratio of copper acetate to potassium iodide is 1:1-15, preferably1:2-10, and more preferably 1:5-8. In some embodiments of the presentinvention, the heat stabilizer is cuprous iodide. The other additive(s)at least comprise antioxidants and/or lubricants.

According to the present invention, the polyamide 56 industrial yarnachieves better heat resistance and mechanical properties by adding theabove-mentioned heat stabilizer during polymerization. The inventorsassume that the reasons might be as follows: firstly, the polyamide 56melt has good fluidity, so the heat stabilizer can be uniformlydistributed in the polyamide 56 resin and has good compatibility withthe polyamide 56 resin. Secondly, the polyamide 56 has a structure in anodd-even carbon arrangement with a high proportion of amide bonds, andsome amide bonds on different molecular chains are not bonded. Afteradding a heat stabilizer containing copper ions, copper ions can play agood complexation function among the amide bonds, therefore the linkagesamong the polyamide 56 molecular chains are more closely, and theintermolecular force is relatively larger, and thus the mechanicalproperties of the prepared industrial yarn are increased.

In some embodiments of the present invention, other additive(s) may alsobe added during the spinning of the polyamide 56 industrial yarn, andthe other additive(s) comprise any one of matting agents, flameretardants, antioxidants, ultraviolet absorbers, infrared absorbers,crystal nucleating agents, fluorescent brighteners and anti-staticagents, or combination thereof; preferably, the other additive(s) areadded in an amount of 0-5 wt %, based on the total weight of productionraw materials.

The antioxidants include, but are not limited to, any one, two, orcombination of commercially available Antioxidant 1010, Antioxidant1098, Antioxidant 168, and sodium hypophosphite. The lubricants include,but are not limited to, commercially available P861/3.5, PTS HOB 7119,and commercially available ET132, ET141 and wax OP.

In Step (1), the polymerization of the polyamide 56 specificallycomprises the following steps:

(1-1) mixing 1,5-pentane diamine, adipic acid and water uniformly underan inert gas or vacuum condition to obtain a polyamide 56 salt solution;wherein the molar ratio of 1,5-pentane diamine to adipic acid is(0.95-1.2): 1; and the inert gas comprises any one of nitrogen, argon orhelium, or combination thereof;

in some embodiments of the present invention, the concentration of thepolyamide 56 salt solution is between 40% and 85%;

(1-2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 0.3-2.5 MPa, degassing, maintaining the pressure,then reducing the pressure in the reaction system to 0-0.2 MPa, andevacuating to a vacuum degree of −(0.01-0.1) MPa (gauge pressure) toobtain a polyamide 56 melt;

wherein preferably, the temperature of the reaction system at the end ofthe pressure-maintenance is 230-275° C.; and/or

preferably, the temperature of the reaction system at the end of thepressure-reduction is 240-285° C.; and/or

preferably, the temperature at the end of evacuation is 265-295° C.

In some embodiments of the present invention, in Step (1), thelow-viscosity polyamide 56 resin in 96% sulfuric acid has a relativeviscosity of 2.0-2.7, preferably 2.2-2.6, and more preferably 2.4-2.5.

In some embodiments of the present invention, in Step (1), thehigh-viscosity polyamide 56 resin in 96% sulfuric acid has a relativeviscosity of 2.7-4.5, preferably 3.2-4.0, and more preferably 3.4-3.6;and/or, the high-viscosity polyamide 56 resin has an oligomer content of0.2-1.0 wt %, and preferably 0.4-0.6 wt %; and/or, the high-viscositypolyamide 56 resin has a number average molecular weight of18,000-40,000, and preferably 25,000-30,000, and/or has a molecularweight distribution of 0.8-1.8, and preferably 1.2-1.5; and/or

in some embodiments of the present invention, the high-viscositypolyamide 56 resin has a moisture content of 200-800 ppm, preferably300-750 ppm, more preferably 350-700 ppm, and further more preferably400-600 ppm; and/or, the high-viscosity polyamide 56 resin has an aminocontent of 20-50 mmol/kg, preferably 24-45 mmol/kg, more preferably28-40 mmol/kg, and further more preferably 32-36 mmol/kg.

In some embodiments of the present invention, the heating in Step (1) iscarried out in a screw extruder, and the screw extruder includes fiveheating zones; wherein the temperature of a first zone is 250-290° C.,the temperature of a second zone is 260-300° C., the temperature of athird zone is 270-320° C., the temperature of a fourth zone is 280-330°C., and the temperature of a fifth zone is 280-320° C.

In some embodiments of the present invention, the spinning process inStep (2) comprises the following steps: ejecting the polyamide 56 resinthrough the spinneret plate of the spinning beam to form the as-spunyarn.

Preferably, the temperature of the spinning beam is 270-330° C., morepreferably 280-310° C., further more preferably 290-300° C., and stillfurther more preferably 293-297° C.; and/or, the pressure of the spinpack of the spinning beam is 8-25 MPa, preferably 12-20 MPa, furthermore preferably 15-18 MPa; and/or, the drawing ratio of the spinneret ofthe spinneret plate is 50-400, preferably 70-300, further morepreferably 80-200, and still further more preferably 90-100.

In some embodiments of the present invention, in Step (3), theprocessing process comprises the following step: thermally insulating,cooling, spin finishing, drawing, and winding into a shape the as-spunyarn which comes out of the spinneret orifices to obtain the polyamide56 industrial yarn;

preferably, the thermal insulating is performed with a slow coolingdevice, the slow cooling temperature is 150-280° C., and more preferably200-240° C., and the slow cooling length is 10-80 mm, and morepreferably 20-50 mm; the cooling is performed with quench air, the airspeed of the quench air is 0.3-2.0 m/s, and more preferably 0.6-1.5 m/s;the air temperature of the quench air is 15-25° C., more preferably17-23° C., and further more preferably 19-22° C.; and/or the humidity ofthe quench air is 60-80%, and more preferably 65-75%; and/or

the winding tension during winding the as-spun yarn into a shape is50-300 cN, preferably 80-200 cN, further more preferably 100-160 cN, andstill further more preferably 120-140 cN; or, the winding speed is2,000-3,800 m/min, preferably 2,500-3,500 m/min, further more preferably2,800-3,000 m/min; and/or the winding overfeed ratio is 5% or less,preferably 4% or less, and further more preferably 3% or less.

In some embodiments of the present invention, the drawing is performedin four or more stages; preferably, the drawing process comprises:firstly, feeding the as-spun yarn, which has been spin finished, to afirst pair of hot rollers through a godet roller, and performing afirst-stage drawing between the first pair of hot rollers and a secondpair of hot rollers; preforming a second-stage drawing between thesecond pair of hot rollers and a third pair of hot rollers; performing athird-stage drawing and a first thermal setting between the third pairof hot rollers and a fourth pair of hot rollers; and then performing afourth-stage drawing and a second thermal setting between the fourthpair of hot rollers and a fifth pair of hot rollers;

wherein preferably the total drawing ratio is 4.0-6.0;

the temperature of the first thermal setting is 180-250° C., andpreferably 200-240° C.; and/or

the temperature of the second thermal setting is 200-240° C., andpreferably 220-230° C.

Advantageous effects of technical solutions according to the presentinvention include:

Firstly, the raw materials for producing the polyamide 5X industrialyarn of the present invention are green materials prepared by abiological process. They neither depend on petroleum resources, norcause serious pollution to the environment. Therefore, carbon dioxideemission and greenhouse effect can be reduced.

Secondly, the polyamide 5X industrial yarn of the present invention hasgood heat resistance, mechanical properties and dimensional stability.

Thirdly, in the process for producing the polyamide 5X industrial yarnaccording to the present invention, a heat stabilizer can be addedduring polymerization and thus the polymerization is an in-situpolymerization. Upon sufficiently mixing, the heat stabilizer can evenlydistribute in the polyamide 5X resin and does not influence spinning.Moreover, filament breaks extremely rare, and the production yield isincreased.

Fourthly, the polyamide 5X industrial yarn according to the presentinvention can be prepared by directly using conventional devices forproducing polyamide 6 and polyamide 66, without modifying thoseconventional spinning devices. Instead, by optimizing the quality of thepolyamide 5X resin and the spinning process, the production yield can beincreased, and the production costs can be reduced, which means hugebenefits for spinning manufacturers.

Mode of Carrying Out the Invention

In order to make the objects, technical solutions and advantages of thepresent invention clearer, the technical solutions in the Examples ofthe present invention will be clearly and completely describedhereinafter with reference to the Examples. Obviously, the Examplesdescribed are only a part but not all of the Examples of the presentinvention. All other Examples obtained by those of ordinary skill in theart based on the Examples in the present invention and without involvingcreative work shall fall within the protection scopes of the presentinvention.

Properties of the products obtained in the following Examples andComparative Examples are measured according to the following methods:

(1) Fineness: measured according to GB/T 14343.

(2) Break Strength: measured according to GB/T 14344-2008.

(3) Elongation at Break: measured according to GB/T 14344-2008.

(4) Heat-resistant Break Strength Retention Rate: heat-resistant breakstrength retention rate=((break strength before heat treatment−breakstrength after heat treatment)/ break strength before heattreatment)*100%. Break strength is measured according to GB/T14344-2008. An oven is used as the heat treatment equipment. The oventemperature is 180° C., and the treatment time is 4 hrs (hours); or theoven temperature is 230° C., and the treatment time is 30 mins(minutes).

(5) Dry Heat Shrinkage: measured according to FZ/T 50004, with the heattreatment temperature being 180° C.

(6) Shrinkage in Boiling Water: measured according to GB/6505-2008“Testing Method for Thermal Shrinkage of Man-Made Filament Yarns”.Specifically, taking a section of polyamide industrial yarn,pre-applying a tension of 0.05±0.005 cN/dtex, marking two points whichare 50.00 cm apart from each other, wrapping it with gauze, putting itinto boiling water and boiling it for 30 mins, and then drying thesample, measuring the length between the two marked points, and usingthe following equation to calculate the shrinkage in boiling water:

Shrinkage in Boiling Water=((initial length−length aftershrinkage)/initial length)* 100%.

(7) Relative Viscosity: The relative viscosity of the oil-free polyamideyarn (unfinished, as-spun yarn) and that of the resin are measured withan Ubbelohde viscometer by a concentrated sulfuric acid process in thefollowing steps: precisely weighing 0.25±0.0002 g sample of the driedpolyamide resin or the staple fiber thereof, adding 50 mL concentratedsulfuric acid (96%) for dissolution, and measuring and recording theflow time to of the concentrated sulfuric acid and the flow time t ofthe sample solution of the polyamide 56 chip or its staple fiber in awater bath at a constant temperature of 25° C.

Relative viscosity is calculated according to the following equation:

Relative Viscosity VN=t/t ₀;

t represents the flow time of the solution; and

t₀ represents the flow time of the solvent.

(8) Moisture content: measured by a Karl Fischer moisture titrator.

(9) Crystallinity and Orientation Degree: A fiber sample is analyzed byusing a D/max-2550 PC X-ray diffractometer manufactured by RigakuCorporation, Japan under the following conditions: a Cu targetwavelength λ_(k) _(a1) =1.54056 Å, a voltage of 20-40 kV, a current of10-450 mA, and a measurement angle 20 in the range of 5-40°. Thepolyamide 56 industrial yarn sample used for measuring the crystallinityis sufficiently shredded, and the mass of the sample is greater than 0.2g. The polyamide 56 industrial yarn sample used for measuring themicrocrystalline orientation was sufficiently combed and tested, withthe bundle length being 30 mm. Softwares such as Origin are used fordata processing so as to analyze and calculate the crystallinity and theorientation degree of the fibers.

The following equation is used for calculating the crystallinity:

${x = {\frac{\sum I_{c}}{{\sum I_{c}} + {\sum I_{a}}} \times 100\%}};$

wherein ΣI^(c) is the total diffraction integral intensity of thecrystalline portions; and

ΣI_(a) is the scattering integral intensity of the amorphous portions.

The following equation is used for calculating the orientation degree:

${y = \frac{360 - {\sum H_{i}}}{360}};$

where H_(i) is a half-height peak width of the i^(th) peak.

(10) Production Yield:

Production Yield=((total amount of the resin charged−amount of thefinished product)/total amount of the resin charged)*100%.

(11) Number Average Molecular Weight: measured by standard GPC.

(12) Molecular Weight Distribution: measured by gel permeationchromatography (GPC).

(13) Oligomer Content: measured by a Water Extraction Method(gravimetry) as follows: about 8 g of polyamide 56 resin, which has beendried at 130° C. for 7 hours, is precisely weighed and placed into a 500mL round bottom flask. 400 g of water is added. After refluxing for 36hours in a heating mantle, the solution is decanted. The particles aredried at 130° C. in a constant-weight beaker for 7 hours, and thensealed into an aluminum-plastic bag to cool down, and weighed. Theweight loss is calculated. The polyamide 56 resin is prepared accordingto the methods disclosed in CN108503826A and CN108503824A, and has arelative viscosity of 2.7-4.5.

(14) Amino content: measuring with an automatic titrator.

(15) Filament Breakage: manually counting the times of filament breakageduring spinning.

(16) Production Yield: the weight percentage of the industrial yarnobtained after spinning based on the weight of the resin charged.

In the following Examples and Comparative Examples, the absolute valueof the difference between the relative viscosity of the oil-free yarnand the relative viscosity of its original resin, the absolute value ofthe difference between the amino content of the oil-free yarn and theamino content of its original resin, the filament breakage (times/24 hr)and the production yield (%) are shown in Table 1 below. The propertiesof the obtained polyamide 56 industrial yarns are shown in Table 2below.

EXAMPLE 1 Polyamide 56 Industrial Yarn (933dtex/140f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding copper acetate as aheat stabilizer in an amount of 200 ppm based on the total weight of theraw materials to obtain a polyamide 56 salt solution with aconcentration of 60%; wherein the molar ratio of 1,5-pentane diamine toadipic acid was1.05:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.2 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 265° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 275° C., and evacuating to avacuum degree of −0.05 MPa with the temperature at the end of evacuationbeing 285° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 155° C., and the drying time was 20hours; the low-viscosity polyamide 56 resin in 96% sulfuric acid had arelative viscosity of 2.4; the high-viscosity polyamide 56 resin in 96%sulfuric acid had a relative viscosity of 3.3, an oligomer content of0.8 wt %, a number average molecular weight of 30,000, a molecularweight distribution of 1.6, a moisture content of 400 ppm, and an aminocontent of 36.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder included five heating zones,wherein the temperature of a first zone was 255° C., the temperature ofa second zone was 270° C., the temperature of a third zone was 280° C.,the temperature of a fourth zone was 290° C., and the temperature of afifth zone was 300° C.; ejecting the polyamide 56 melt through thespinneret plate of the spinning beam to form an as-spun yarn; whereinthe temperature of the spinning beam was 290° C., the pressure of thepack was 15 MPa, and the drawing ratio of the spinneret was 150;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn;

the thermal insulation was performed with a slow cooling device, theslow cooling temperature was 220° C., and the slow cooling length was 20mm;

the cooling was performed with quench air, and the air speed was 1.2m/s; the air temperature was 22° C.; and the humidity was 70%.

The drawing was performed in four stages comprising: firstly, feedingthe as-spun yarn, which had been spin finished, to a first pair of hotrollers through a godet roller; performing a first-stage drawing betweenthe first pair of hot rollers and a second pair of hot rollers;preforming a second-stage drawing between the second pair of hot rollersand a third pair of hot rollers; performing a third-stage drawing and afirst thermal setting between the third pair of hot rollers and a fourthpair of hot rollers; and then performing a fourth-stage drawing and asecond thermal setting between the fourth pair of hot rollers and afifth pair of hot rollers; wherein the total drawing ratio was 5.0; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C. The windingtension during winding the as-spun yarn into a shape was 90 cN; thewinding speed was 3,500 m/min; and the winding overfeed ratio was 2%.

EXAMPLE 2 Polyamide 56 Industrial Yarn (830 dtex/192f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding copper acetate as aheat stabilizer in an amount of 500 ppm based on the total weight of theraw materials to obtain a polyamide 56 salt solution with aconcentration of 60%; wherein the molar ratio of 1,5-pentane diamine toadipic acid was 1.1:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.3 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 255° C., reducing the pressure in thereaction system to 0 MPa with the temperature of the reaction system atthe end of the pressure reduction being 265° C., and evacuating to avacuum degree of −0.08 MPa with the temperature at the end of evacuationbeing 275° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature forthe solid phase tackifying was 160° C., and the drying time was 18hours; the low-viscosity polyamide 56 resin in 96% sulfuric acid had arelative viscosity of 2.5; the high-viscosity polyamide 56 resin in 96%sulfuric acid had a relative viscosity of 3.5, an oligomer content of0.6 wt %, a number average molecular weight of 33,000, a molecularweight distribution of 1.5, a moisture content of 450 ppm, and an aminocontent of 33.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder included in particular fiveheating zones, wherein the temperature of a first zone was 265° C., thetemperature of a second zone was 275° C., the temperature of a thirdzone was 285° C., the temperature of a fourth zone was 295° C., and thetemperature of a fifth zone was 305° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 295° C., thepressure of the pack was 18 MPa and the drawing ratio of the spinneretwas 180;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 230° C., and theslow cooling length was 30 mm; the cooling was performed with quenchair, and the air speed was 0.8 m/s; the air temperature was 23° C.; andthe humidity was 75%; the winding tension during winding the as-spunyarn into a shape was 80 cN; the winding speed was 3,000 m/min; and thewinding overfeed ratio was 3%. The drawing process was four-stagedrawing process which was the same as that in Example 1, except that thetotal drawing ratio was 4.8; the temperature of the first thermalsetting was 225° C.; and the temperature of the second thermal settingwas 240° C.

EXAMPLE 3 Polyamide 56 Industrial Yarn (550 dtex/96f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding cuprous iodide as aheat stabilizer in an amount of 150 ppm based on the total weight of theraw materials to obtain a polyamide 56 salt solution with aconcentration of 65%; wherein the molar ratio of 1,5-pentane diamine toadipic acid was 1.1:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.3 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 240° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 270° C., and evacuating to avacuum degree of −0.05 MPa with the temperature at the end of evacuationbeing 280° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 160° C., and the drying time was 22hours;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.6; the high-viscosity polyamide 56 resin in 96% sulfuricacid had a relative viscosity of 3.0, an oligomer content of 0.8 wt %, anumber average molecular weight of 30,000, a molecular weightdistribution of 1.6, a moisture content of 400 ppm, and an amino contentof 42.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 248° C.,the temperature of a second zone was 263° C., the temperature of a thirdzone was 276° C., the temperature of a fourth zone was 285° C., and thetemperature of a fifth zone was 293° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form the as-spunyarn; wherein the temperature of the spinning beam was 285° C., thepressure of the pack was 16 MPa and the drawing ratio of the spinneretwas 100;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 220° C., and theslow cooling length was 25 mm; the cooling was performed with quenchair, and the air speed was 1.4 m/s; the air temperature was 22° C.; andthe humidity was 65%; the winding tension during winding the as-spunyarn into a shape was 55 cN; the winding speed was 2,800 m/min; and thewinding overfeed ratio was 2.5%. The drawing process was four-stagedrawing process which was the same as that in Example 1, except that thetotal drawing ratio was 5.0; the temperature of the first thermalsetting was 220° C.; and the temperature of the second thermal settingwas 235° C.

EXAMPLE 4 Polyamide 56 Industrial Yarn (550 dtex/96f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding cuprous iodide as aheat stabilizer in an amount of 250 ppm based on the total weight of theraw materials to obtain a polyamide 56 salt solution with aconcentration of 65%; wherein the molar ratio of 1,5-pentane diamine toadipic acid was 1.12:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.4 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 245° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 275° C., and evacuating to avacuum degree of −0.07 MPa with the temperature at the end of evacuationbeing 280° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 150° C., and the drying time was 25hours; the low-viscosity polyamide 56 resin in 96% sulfuric acid had arelative viscosity of 2.55; the high-viscosity polyamide 56 resin in 96%sulfuric acid had a relative viscosity of 2.9, an oligomer content of0.8 wt %, a number average molecular weight of 28,000, a molecularweight distribution of 1.5, a moisture content of 300 ppm, and an aminocontent of 40.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 245° C.,the temperature of a second zone was 260° C., the temperature of a thirdzone was 270° C., the temperature of a fourth zone was 285° C., and thetemperature of a fifth zone was 290° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 280° C., thepressure of the pack was 10 MPa and the drawing ratio of the spinneretwas 200;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 210° C., and theslow cooling length was 25mm; the cooling was performed with quench air,and the air speed was 1.3 m/s; the air temperature was 24° C.; and thehumidity was 65%; the winding tension during winding the as-spun yarninto a shape was 55 cN; the winding speed was 2,600 m/min; and thewinding overfeed ratio was 2.5%. The drawing process was four-stagedrawing process which was the same as that in Example 1, except that thetotal drawing ratio was 5.3; the temperature of the first thermalsetting was 225° C.; and the temperature of the second thermal settingwas 235° C.

EXAMPLE 5 Polyamide 56 Industrial Yarn (233 dtex/36f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding cuprous iodide as aheat stabilizer in an amount of 400 ppm based on the total weight of theraw materials to obtain a polyamide 56 salt solution with aconcentration of 65%; wherein the molar ratio of 1,5-pentane diamine toadipic acid was 1.05:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.0 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 260° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 275° C., and evacuating to avacuum degree of −0.08 MPa with the temperature at the end of evacuationbeing 295° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 155° C., and the drying time was 25hours;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.45; the high-viscosity polyamide 56 resin in 96% sulfuricacid had a relative viscosity of 3.6, an oligomer content of 1.0 wt %, anumber average molecular weight of 36,000, a molecular weightdistribution of 1.7, a moisture content of 350 ppm, and an amino contentof 46.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 255° C.,the temperature of a second zone was 275° C., the temperature of a thirdzone was 280° C., the temperature of a fourth zone was 295° C., and thetemperature of a fifth zone was 310° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 295° C., thepressure of the pack was 19 MPa and the drawing ratio of the spinneretwas 250;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 220° C., and theslow cooling length was 20 mm; the cooling was performed with quenchair, and the air speed was 1.0 m/s; the air temperature was 18° C.; andthe humidity was 70%; the winding tension during winding the as-spunyarn into a shape was 23 cN; the winding speed was 2,900 m/min; and thewinding overfeed ratio was 1.5%. The drawing process was four-stagedrawing process which was the same as that in Example 1, except that thetotal drawing ratio was 5.5; the temperature of the first thermalsetting was 230° C.; and the temperature of the second thermal settingwas 230° C.

EXAMPLE 6 Polyamide 56 Industrial Yarn (1,670 dtex/192f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding a heat stabilizer toobtain a polyamide 56 salt solution with a concentration of 65%; whereinthe molar ratio of 1,5-pentane diamine to adipic acid was 1.1:1; theheat stabilizer was a composite of copper acetate and potassium iodide,wherein copper acetate was added in an amount of 200 ppm based on thetotal weight of the production raw materials, and potassium iodide wasadded in an amount of 500 ppm based on the total weight of theproduction raw materials.

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.3 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 255° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 270° C., and evacuating to avacuum degree of −0.01 MPa with the temperature at the end of evacuationbeing 280° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 155° C., and the drying time was 30hours;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.7; the high-viscosity polyamide 56 resin in 96% sulfuricacid had a relative viscosity of 3.8, an oligomer content of 0.8 wt %, anumber average molecular weight of 38,000, a molecular weightdistribution of 1.5, a moisture content of 500 ppm, and an amino contentof 42.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 250° C.,the temperature of a second zone was 275° C., the temperature of a thirdzone was 280° C., the temperature of a fourth zone was 295° C., and thetemperature of a fifth zone was 305° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 290° C., thepressure of the pack was 14 MPa and the drawing ratio of the spinneretwas 120;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 230° C., and theslow cooling length was 40 mm; the cooling was performed with quenchair, and the air speed was 1.1 m/s; the air temperature was 23° C.; andthe humidity was 75%; the winding tension during winding the as-spunyarn into a shape was 160 cN;

the winding speed was 3,200 m/min; and the winding overfeed ratio was3.5%. The drawing process was four-stage drawing process which was thesame as that in Example 1, except that the total drawing ratio was 5.6;the temperature of the first thermal setting was 225° C.; and thetemperature of the second thermal setting was 235° C.

EXAMPLE 7 Polyamide 56 Industrial Yarn (2,800 dtex/480f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding a heat stabilizer toobtain a polyamide 56 salt solution with a concentration of 65%; whereinthe molar ratio of 1,5-pentane diamine to adipic acid was 1.05:1; theheat stabilizer was a composite of copper acetate and potassium iodide,wherein copper acetate was added in an amount of 250 ppm based on thetotal weight of the production raw materials, and potassium iodide wasadded in an amount of 2,000 ppm based on the total weight of theproduction raw materials.

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.2 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 260° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 285° C., and evacuating to avacuum degree of −0.03 MPa with the temperature at the end of evacuationbeing 290° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 155° C., and the drying time was 30hours;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.35; the high-viscosity polyamide 56 resin in 96% sulfuricacid had a relative viscosity of 3.2, an oligomer content of 0.8 wt %, anumber average molecular weight of 32,000, a molecular weightdistribution of 1.5, a moisture content of 450 ppm, and an amino contentof 38.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 258° C.,the temperature of a second zone was 276° C., the temperature of a thirdzone was 288° C., the temperature of a fourth zone was 298° C., and thetemperature of a fifth zone was 305° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 293° C., thepressure of the pack was 12 MPa and the drawing ratio of the spinneretwas 160;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 230° C., and theslow cooling length was 20 mm; the cooling was performed with quenchair, and the air speed was 1.2 m/s; the air temperature was 23° C.; andthe humidity was 70%; the winding tension during winding the as-spunyarn into a shape was 280 cN; the winding speed was 2,700 m/min; and thewinding overfeed ratio was 3%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 4.8; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C.

EXAMPLE 8 Polyamide 56 Industrial Yarn (233 dtex/36f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding a heat stabilizer toobtain a polyamide 56 salt solution with a concentration of 65%; whereinthe molar ratio of 1,5-pentane diamine to adipic acid was 1.05:1; theheat stabilizer was a composite of copper acetate and potassium iodide,wherein copper acetate was added in an amount of 150 ppm based on thetotal weight of the production raw materials, and potassium iodide wasadded in an amount of 800 ppm based on the total weight of theproduction raw materials.

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.2 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 260° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 285° C., and evacuating to avacuum degree of −0.01 MPa with the temperature at the end of evacuationbeing 290° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 155° C., and the drying time was 30hours;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.4; the high-viscosity polyamide 56 resin in 96% sulfuricacid had a relative viscosity of 3.4, an oligomer content of 0.8 wt %, anumber average molecular weight of 33,000, a molecular weightdistribution of 1.6, a moisture content of 550 ppm, and an amino contentof 33.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 268° C.,the temperature of a second zone was 280° C., the temperature of a thirdzone was 290° C., the temperature of a fourth zone was 295° C., and thetemperature of a fifth zone was 303° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 298° C., thepressure of the pack was 18 MPa and the drawing ratio of the spinneretwas 120;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 220° C., and theslow cooling length was 30 mm; the cooling was performed with quenchair, and the air speed was 1.2 m/s; the air temperature was 23° C.; andthe humidity was 70%; the winding tension during winding the as-spunyarn into a shape was 140 cN; the winding speed was 3,000 m/min; and thewinding overfeed ratio was 2%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 4.8; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C.

EXAMPLE 9 Polyamide 56 Industrial Yarn (933 dtex/140f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding copper chloride as aheat stabilizer in an amount of 300 ppm based on the total weight of theraw materials to obtain a polyamide 56 salt solution with aconcentration of 65%; wherein the molar ratio of 1,5-pentane diamine toadipic acid was 1.1:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.25 MPa, degassing, maintaining the pressurewith the temperature of the reaction system at the end of thepressure-maintenance being 260° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 275° C., and evacuating to avacuum degree of −0.01 MPa with the temperature at the end of evacuationbeing 280° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 160° C., and the drying time was 22hours;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.4; the high-viscosity polyamide 56 resin in 96% sulfuricacid had a relative viscosity of 3.4, an oligomer content of 0.8 wt %, anumber average molecular weight of 33,000, a molecular weightdistribution of 1.6, a moisture content of 550 ppm, and an amino contentof 33.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 268° C.,the temperature of a second zone was 280° C., the temperature of a thirdzone was 290° C., the temperature of a fourth zone was 295° C., and thetemperature of a fifth zone was 303° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 280° C., thepressure of the pack was 13 MPa and the drawing ratio of the spinneretwas 150;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 200° C., and theslow cooling length was 40 mm; the cooling was performed with quenchair, and the air speed was 1.3 m/s; the air temperature was 20° C.; andthe humidity was 70%; the winding tension during winding the as-spunyarn into a shape was 90 cN; the winding speed was 2,700 m/min; and thewinding overfeed ratio was 2.5%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 4.8; thetemperature of the first thermal setting was 210° C.; and thetemperature of the second thermal setting was 220° C.

EXAMPLE 10 Polyamide 56 Industrial Yarn (933 dtex/140f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition to obtain a polyamide 56 saltsolution with a concentration of 65%; wherein the molar ratio of1,5-pentane diamine to adipic acid was 1.15:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.3 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 265° C., reducing the pressure in thereaction system to 0 MPa with the temperature of the reaction system atthe end of the pressure reduction being 275° C., and evacuating to avacuum degree of −0.04 MPa with the temperature at the end of evacuationbeing 285° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

the heat stabilizer masterbatch was injected online before the polymermelt was pelletized, the copper ion content in the heat stabilizermasterbatch was 2.0 wt %, and the addition amount of the heat stabilizermasterbatch was 1.5 wt %; the heat stabilizer masterbatch base materialwas polyamide 56; the process for producing the heat stabilizermasterbatch comprised the following steps: (a) drying the base materialpolyamide 56 in vacuum, and then grinding it into powders; the polyamide56 was 65 parts by weight, the relative viscosity thereof was 2.9, thenumber average molecular weight thereof was 24 kg/mol, the molecularweight distribution thereof was 2.1, and the moisture content thereofwas 500 ppm; (b) mixing the powders obtained in Step (a) with 12.5 partsby weight of heat stabilizer cuprous iodide, 0.5 parts by weight oflubricant Wax OP, 0.2 parts by weight of Antioxidant 168, melting,extruding and pelletizing the mixture with a twin-screw to obtain a heatstabilizer masterbatch, wherein the processing temperature of each zonewas set as follows: the temperature of a first zone was 251° C., thetemperature of a second zone was 264° C., the temperature of a thirdzone was 269° C., the temperature of a fourth zone was 273° C., and thetemperature of a fifth zone was 276° C.; the screw rotation speed was250 r/min, and the filter screen was 150 mesh.

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 155° C., and the drying time was 25hours;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.5; the high-viscosity polyamide 56 resin in 96% sulfuricacid had a relative viscosity of 3.7, an oligomer content of 0.6 wt %, anumber average molecular weight of 34,000, a molecular weightdistribution of 1.5, a moisture content of 300 ppm, and an amino contentof 33.8 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 265° C.,the temperature of a second zone was 278° C., the temperature of a thirdzone was 288° C., the temperature of a fourth zone was 295° C., and thetemperature of a fifth zone was 300° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 295° C., thepressure of the pack was 14 MPa and the drawing ratio of the spinneretwas 80;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 230° C., and theslow cooling length was 25 mm; the cooling was performed with quenchair, and the air speed was 1.1 m/s; the air temperature was 22° C.; andthe humidity was 70%;

the winding tension during winding the as-spun yarn into a shape was 90cN; the winding speed was 2,600 m/min; and the winding overfeed ratiowas 2%.

the drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 5.0; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C.

EXAMPLE 11 Polyamide 56 Industrial Yarn (933 dtex/140f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition to obtain a polyamide 56 saltsolution with a concentration of 65%; wherein the molar ratio of1,5-pentane diamine to adipic acid was 1.06:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.2 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 265° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 275° C., and evacuating to avacuum degree of −0.06 MPa with the temperature at the end of evacuationbeing 285° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 160° C., and the drying time was 28hours; the low-viscosity polyamide 56 resin in 96% sulfuric acid had arelative viscosity of 2.4; the high-viscosity polyamide 56 resin in 96%sulfuric acid had a relative viscosity of 3.3, an oligomer content of0.9 wt %, a number average molecular weight of 32,000, a molecularweight distribution of 1.6, a moisture content of 450 ppm, and an aminocontent of 36.5 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 255° C.,the temperature of a second zone was 275° C., the temperature of a thirdzone was 280° C., the temperature of a fourth zone was 290° C., and thetemperature of a fifth zone was 305° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 295° C., thepressure of the pack was 14 MPa and the drawing ratio of the spinneretwas 140;

a heat stabilizer masterbatch was blended with a masterbatch additiondevice during the spinning, the content of copper ions in the heatstabilizer masterbatch was 1.8 wt %; the heat stabilizer masterbatch wasadded in an amount of 1.2 wt %; and the process for producing the heatstabilizer masterbatch was the same as that in Example 10.

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 240° C., and theslow cooling length was 20 mm; the cooling was performed with quenchair, and the air speed was 1.4 m/s; the air temperature was 22° C.; andthe humidity was 70%;

the winding tension during winding the as-spun yarn into a shape was 90cN; the winding speed was 3,500 m/min; and the winding overfeed ratiowas 2%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 5.0; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C.

EXAMPLE 12 Polyamide 56 Industrial Yarn (933 dtex/140f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition to obtain a polyamide 56 saltsolution with a concentration of 65%; wherein the molar ratio of1,5-pentane diamine to adipic acid was 1.08:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.2 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 265° C., reducing the pressure in thereaction system to 0 MPa with the temperature of the reaction system atthe end of the pressure reduction being 275° C., and evacuating to avacuum degree of −0.05 MPa with the temperature at the end of evacuationbeing 290° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

(3) solid phase tackifying the low-viscosity polyamide 56 resin toprepare a high-viscosity polyamide 56 resin; wherein the temperature ofthe solid phase tackifying was 160° C., and the drying time was 28hours; the low-viscosity polyamide 56 resin in 96% sulfuric acid had arelative viscosity of 2.4; the high-viscosity polyamide 56 resin in 96%sulfuric acid had a relative viscosity of 3.2, an oligomer content of0.8 wt %, a number average molecular weight of 30,000, a molecularweight distribution of 1.6, a moisture content of 400 ppm, and an aminocontent of 32.3 mmol/kg.

2. Spinning:

(1) heating the high-viscosity polyamide 56 resin into a molten state soas to form a polyamide 56 melt, wherein the heating was carried out in ascrew extruder, and the screw extruder was in particular divided intofive heating zones, wherein the temperature of a first zone was 250° C.,the temperature of a second zone was 270° C., the temperature of a thirdzone was 285° C., the temperature of a fourth zone was 290° C., and thetemperature of a fifth zone was 290° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 285° C., thepressure of the pack was 12 MPa and the drawing ratio of the spinneretwas 180;

a heat stabilizer masterbatch was blended with a masterbatch additiondevice during the spinning, the content of copper ions in the heatstabilizer masterbatch was 1.6 wt %, and the heat stabilizer masterbatchwas added in an amount of 1.5 wt %;

the heat stabilizer masterbatch base material was polyamide 6; theprocess for producing the heat stabilizer masterbatch comprised thefollowing steps: (a) drying the base material polyamide 6 in vacuum, andthen grinding it into powders; the polyamide 6 was 65 parts by weight,the relative viscosity thereof was 2.9, the number average molecularweight thereof was 24 kg/mol, the molecular weight distribution thereofwas 2.1, and the moisture content thereof was 500 ppm; (b) mixing thepowders obtained in Step (a) with 15 parts by weight of heat stabilizercuprous iodide, 0.5 parts by weight of lubricant Wax OP, 0.2 parts byweight of Antioxidant 168, melting, extruding and pelletizing themixture with a twin-screw to obtain a heat stabilizer masterbatch,wherein the processing temperature of each zone was set as follows: thetemperature of a first zone was 200° C., the temperature of a secondzone was 210° C., the temperature of a third zone was 220° C., thetemperature of a fourth zone was 230° C., and the temperature of a fifthzone was 235° C., the screw rotation speed was 250 r/min, and the filterscreen was 150 mesh.

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 225° C., and theslow cooling length was 20 mm; the cooling was performed with quenchair, and the air speed was 1.2 m/s; the air temperature was 22° C.; andthe humidity was 70%;

the winding tension during winding the as-spun yarn into a shape was 90cN; the winding speed was 3,300 m/min; and the winding overfeed ratiowas 2%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 5.0; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C.

EXAMPLE 13 Polyamide 56 Industrial Yarn (933 dtex/140f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding cuprous iodide as aheat stabilizer in an amount of 200 ppm based on the total weight of theraw materials to obtain a polyamide 56 salt solution with aconcentration of 65%; wherein the molar ratio of 1,5-pentane diamine toadipic acid was 1.1:1;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.25 MPa, degassing, maintaining the pressurewith the temperature of the reaction system at the end of thepressure-maintenance being 265° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 280° C., and evacuating to avacuum degree of −0.01 MPa with the temperature at the end of evacuationbeing 295° C. to directly obtain a high-viscosity polyamide 56 resin;wherein all the pressures are gauge pressures; the high-viscositypolyamide 56 melt in 96% sulfuric acid had a relative viscosity of 3.4,an oligomer content of 0.8 wt %, a number average molecular weight of30,000, a molecular weight distribution of 1.6, a moisture content of400 ppm, and an amino content of 32.5 mmol/kg.

2. Spinning:

(1) conveying the high-viscosity polyamide 56 melt to a spinning beam bya melt booster pump, and spinning directly; ejecting the polyamide 56melt through the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 280° C., thepressure of the pack was 18 MPa and the drawing ratio of the spinneretwas 200;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 220° C., and theslow cooling length was 20 mm; the cooling was performed with quenchair, and the air speed was 1.2 m/s; the air temperature was 22° C.; andthe humidity was 70%;

the winding tension during winding the as-spun yarn into a shape was 90cN; the winding speed was 2,500 m/min; and the winding overfeed ratiowas 2%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 5.0; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C.

EXAMPLE 14 Polyamide 56 Industrial Yarn (2,800 dtex/480f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding a heat stabilizer toobtain a polyamide 56 salt solution with a concentration of 65%; whereinthe molar ratio of 1,5-pentane diamine to adipic acid was 1.08:1; theheat stabilizer was a composite of copper acetate and potassium iodide,wherein copper acetate was added in an amount of 200 ppm based on thetotal weight of the production raw materials, and potassium iodide wasadded in an amount of 700 ppm based on the total weight of theproduction raw materials.

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.4 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 265° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 285° C., and evacuating to avacuum degree of −0.06 MPa with the temperature at the end of evacuationbeing 290° C. to directly obtain a high-viscosity polyamide 56 melt;wherein all the pressures are gauge pressures; the high-viscositypolyamide 56 melt in 96% sulfuric acid had a relative viscosity of 3.5,an oligomer content of 1.0 wt %, a number average molecular weight of34,000, a molecular weight distribution of 1.6, a moisture content of450 ppm, and an amino content of 40.5 mmol/kg.

2. Spinning:

(1) conveying the high-viscosity polyamide 56 melt to a spinning beam bya melt booster pump, and spinning directly; ejecting the polyamide 56melt through the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 290° C., thepressure of the pack was 12 MPa and the drawing ratio of the spinneretwas 180;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 210° C., and theslow cooling length was 20 mm; the cooling was performed with quenchair, and the air speed was 1.2 m/s; the air temperature was 23° C.; andthe humidity was 70%;

the winding tension during winding the as-spun yarn into a shape was 280cN; the winding speed was 2,900 m/min; and the winding overfeed ratiowas 3%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 4.5; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C.

EXAMPLE 15 Polyamide 56 Industrial Yarn (1,670 dtex/192f)

The preparation process was the same as that in Example 6, except thatthe heat stabilizer was a composite of copper acetate and potassiumiodide, wherein copper acetate was added in an amount of 200 ppm basedon the total weight of the production raw materials, and potassiumiodide was added in an amount of 1,000 ppm based on the total weight ofthe production raw materials.

EXAMPLE 16 Polyamide 56 Industrial Yarn (1,670 dtex/192f)

The preparation process was the same as that in Example 6, except thatthe heat stabilizer was a composite of copper acetate and potassiumiodide, wherein copper acetate was added in an amount of 200 ppm basedon the total weight of the production raw materials, and potassiumiodide was added in an amount of 2,000 ppm based on the total weight ofthe production raw materials.

EXAMPLE 17 Polyamide 56 Industrial Yarn (1,670 dtex/192f)

The preparation process was the same as that in Example 6, except thatthe heat stabilizer was a composite of copper acetate and potassiumiodide, wherein copper acetate was added in an amount of 200 ppm basedon the total weight of the production raw materials, and potassiumiodide was added in an amount of 1,800 ppm based on the total weight ofthe production raw materials.

EXAMPLE 18 Polyamide 56 Industrial Yarn (1,670 dtex/192f)

The preparation process was the same as that in Example 6, except thatthe heat stabilizer was a composite of copper acetate and potassiumiodide, wherein copper acetate was added in an amount of 200 ppm basedon the total weight of the production raw materials, and potassiumiodide was added in an amount of 2,500 ppm based on the total weight ofthe production raw materials.

COMPARATIVE EXAMPLE 1 Polyamide 56 Industrial Yarn (933 dtex/140f)

The preparation method was the same as that in Example 1, except thatheat stabilizer copper acetate was not added during the polymerizationof 1,5-pentane diamine and adipic acid in Step (1).

COMPARATIVE EXAMPLE 2 Polyamide 56 Industrial Yarn (933 dtex/140f)

The preparation method was the same as that in Example 1, except thatthe obtained high-viscosity polyamide 56 resin has a moisture content of1,200 ppm in the polymerization in Step 1.

COMPARATIVE EXAMPLE 3 Polyamide 56 Industrial Yarn (1,670 dtex/192f)

The process comprised the following steps:

1. Polymerization:

(1) mixing raw materials 1,5-pentane diamine, adipic acid and wateruniformly under a nitrogen condition, and adding a heat stabilizer toobtain a polyamide 56 salt solution with a concentration of 60%; whereinthe molar ratio of 1,5-pentane diamine to adipic acid was 1.1:1; theheat stabilizer was a composite of copper acetate and potassium iodide,wherein copper acetate was added in an amount of 200 ppm based on thetotal weight of the production raw materials, and potassium iodide wasadded in an amount of 500 ppm based on the total weight of theproduction raw materials;

(2) heating the polyamide 56 salt solution, increasing the pressure inthe reaction system to 2.3 MPa, degassing, maintaining the pressure withthe temperature of the reaction system at the end of thepressure-maintenance being 255° C., reducing the pressure in thereaction system to 0.1 MPa with the temperature of the reaction systemat the end of the pressure reduction being 270° C., and evacuating to avacuum degree of −0.05 MPa with the temperature at the end of evacuationbeing 280° C. to obtain a low-viscosity polyamide 56 resin; wherein allthe pressures are gauge pressures;

the low-viscosity polyamide 56 resin in 96% sulfuric acid had a relativeviscosity of 2.5, an oligomer content of 0.8 wt %, a number averagemolecular weight of 16,000, a molecular weight distribution of 1.5, amoisture content of 500 ppm, and an amino content of 42.5 mmol/kg.

2. Spinning:

(1) heating the low-viscosity polyamide 56 resin to a molten state toform a polyamide 56 melt, wherein the heating was carried out in a screwextruder, and the screw extruder was in particular divided into fiveheating zones, wherein the temperature of a first zone was 250° C., thetemperature of a second zone was 275° C., the temperature of a thirdzone was 280° C., the temperature of a fourth zone was 295° C., and thetemperature of a fifth zone was 305° C.; ejecting the polyamide 56 meltthrough the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 290° C., thepressure of the pack was 14 MPa and the drawing ratio of spinneret was120;

(2) thermally insulating, cooling, spin finishing, drawing, and windingthe as-spun yarn into a shape so as to obtain the polyamide 56industrial yarn; wherein the thermal insulation was performed with aslow cooling device, the slow cooling temperature was 230° C., and theslow cooling length was 40 mm; the cooling was performed with quenchair, and the air speed was 1.1 m/s; the air temperature was 23° C.; andthe humidity was 75%; the winding tension during winding the as-spunyarn into a shape was 160 cN; the winding speed was 3,200 m/min; and thewinding overfeed ratio was 3.5%; the drawing process was four-stagedrawing process which was the same as that in Example 1, except that thetotal drawing ratio was 5.6; the temperature of the first thermalsetting was 225° C.; and the temperature of the second thermal settingwas 235° C.

COMPARATIVE EXAMPLE 4 Polyamide 6 Industrial Yarn (933 dtex/140f)

The process comprised the following steps:

(1) heating the high-viscosity polyamide 6 resin into a molten state toform a polyamide 6 melt, wherein the heating was carried out in a screwextruder, and the screw extruder included in particular five heatingzones, wherein the temperature of a first zone was 255° C., thetemperature of a second zone was 270° C., the temperature of a thirdzone was 280° C., the temperature of a fourth zone was 290° C., and thetemperature of a fifth zone was 300° C.; the high-viscosity polyamide 6resin in 96% sulfuric acid had a relative viscosity of 3.3, an oligomercontent of 0.8 wt %, a number average molecular weight of 30,000, amolecular weight distribution of 1.6, a moisture content of 400 ppm, andan amino content of 36.5 mmol/kg.

2. Spinning the polyamide 6 melt into yarns, ejecting the polyamide 6melt through the spinneret plate of the spinning beam to form an as-spunyarn; wherein the temperature of the spinning beam was 290° C., thepressure of the pack was 15 MPa and the drawing ratio of spinneret was150;

3. processing the as-spun yarn to obtain the polyamide 6 industrialyarn, wherein the processing comprised the steps of thermallyinsulating, cooling, spin finishing, drawing, and winding the as-spunyarn into a shape so as to obtain the polyamide 56 industrial yarn;wherein the thermal insulation was performed with a slow cooling device,the slow cooling temperature was 220° C., and the slow cooling lengthwas 20 mm; the cooling was performed with quench air, and the air speedwas 1.2 m/s; the air temperature was 22° C.; and the humidity was 70%;

the winding tension during winding the as-spun yarn into a shape was 90cN; the winding speed was 3,500 m/min; and the winding overfeed ratiowas 2.0%.

The drawing process was four-stage drawing process which was the same asthat in Example 1, except that the total drawing ratio was 5.0; thetemperature of the first thermal setting was 220° C.; and thetemperature of the second thermal setting was 230° C. In the aboveExamples and Comparative Examples, the absolute value of the differencebetween the relative viscosity of the oil-free yarn and the relativeviscosity of its original resin, the absolute value of the differencebetween the amino content of the oil-free yarn and the amino content ofits original resin, the filament breakage (times/24 hrs) and theproduction yield (%) are shown in Table 1 below. The properties of theobtained polyamide 56 industrial yarn are shown in Table 2 below.

TABLE 1 Absolute value Absolute value of the difference of thedifference Relative between the relative Amino Amino between the aminoviscosity Relative viscosity of the oil- content of content of contentof the oil- Filament of the viscosity of free yarn and the the originalthe oil- free yarn and the breakage Production original the oil-relative viscosity of resin free yarn amino content of (times/ yield No.resin free yarn its original resin (mmol/kg) (mmol/kg) its originalresin 24 hrs) (%) Example 1 3.31 3.40 0.09 36.5 35.2 1.3 1 97.8 Example2 3.52 3.57 0.05 33.5 33.0 0.5 1 96.7 Example 3 3.00 3.06 0.06 42.5 41.01.5 0 96.0 Example4 2.90 3.00 0.10 40.5 39.2 1.3 0 95.2 Example 5 3.603.63 0.03 46.5 45.3 1.2 1 96.3 Example 6 3.41 3.46 0.05 43.2 42.5 0.7 097.0 Example 7 3.21 3.20 0.01 38.5 39.0 0.5 0 98.5 Example 8 3.41 3.490.08 33.5 33.0 0.5 0 96.7 Example 9 3.61 3.66 0.05 34.5 32.0 2.5 1 96.3Example 10 3.70 3.80 0.10 33.8 32.6 1.2 1 96.4 Example 11 3.29 3.37 0.0836.5 35.0 1.5 1 95.8 Example 12 3.22 3.19 0.03 32.3 34.0 1.7 1 95.0Example 13 3.39 3.46 0.07 32.5 30.7 1.8 0 97.2 Example 14 3.50 3.48 0.0240.5 41.8 1.3 0 98.3 Example 15 3.38 3.40 0.02 42.5 41.2 1.3 0 97.0Example 16 3.41 3.46 0.05 42.0 40.8 1.2 0 96.5 Example 17 3.42 3.50 0.0842.5 41.4 1.1 0 98.5 Example 18 3.40 3.44 0.04 42.3 40.8 1.5 0 97.5Comparative 3.32 3.17 0.15 36.5 42.0 5.5 4 90.8 Example 1 Comparative3.31 2.90 0.41 36.5 43.4 6.9 12 80.5 Example 2 Comparative 2.50 2.370.13 42.5 47.8 5.3 15 83.4 Example 3 Comparative 3.30 3.28 0.02 36.539.0 2.5 3 93.0 Example 4

In the present invention, by reducing the viscosity of the oil-free yarnand the fluctuation range of the amino content, uniformity and stabilityof the polyamide 56 melt were increased, the filament breakage wasreduced, and the spinnability were increased. The prepared polyamide 56industrial yarn achieved a high yield of 95% or more, and had a filamentbreakage of 1 time or less every 24 hrs.

TABLE 2 180° C. * 4 hrs; 230° C. * 30 mins; Heat Resistant HeatResistant Break Strength Break Strength Dry Heat Break elongationShrinkage Orientation Retention Retention Shrinkage Strength at break inBoiling Crystallinity Degree No. Rate (%) Rate (%) (%) (cN/dtex) (%)Water (%) (%) (%) Example 1 92.2 91.6 5.2 8.5 23.9 5.8 72.6 82.5 Example2 95.3 93.8 4.8 8.6 22.2 5.5 74.3 84.4 Example 3 92.8 91.6 5.3 8.6 20.85.2 74.7 84.5 Example 4 93.8 92.4 5.1 8.7 19.8 5.0 75.0 85.0 Example 596.2 95.7 4.6 8.8 17.5 4.8 76.4 86.2 Example 6 94.5 94.5 4.5 8.6 20.24.6 75.3 87.8 Example 7 96.9 95.5 4.2 8.8 21.5 4.3 76.8 88.2 Example 893.8 92.0 4.2 8.5 18.0 4.8 74.5 86.9 Example 9 91.5 90.8 5.3 8.6 22.84.7 73.9 85.3 Example 10 92.6 92.0 4.9 8.6 20.5 5.0 73.4 82.3 Example 1193.8 93.5 5.2 8.5 19.8 5.5 74.3 84.8 Example 12 92.4 92.2 5.3 8.4 18.45.6 72.4 83.1 Example 13 94.2 93.8 4.7 8.7 21.2 4.9 76.0 82.6 Example 1495.4 94.6 5.0 8.5 22.3 5.2 75.2 84.5 Example 15 94.7 93.9 4.6 8.6 21.04.5 74.9 87.5 Example 16 95.1 94.8 4.4 8.6 19.3 4.4 75.1 87.3 Example 1794.5 93.1 4.7 8.5 22.2 4.8 74.9 83.5 Example 18 92.9 91.3 4.7 8.6 19.04.5 71.3 81.7 Comparative 70.5 68.5 8.0 7.6 20.0 8.2 68.5 72.5 Example 1Comparative 85.6 82.9 7.0 6.3 22.6 8.1 63.2 70.7 Example 2 Comparative82.2 80.7 7.5 6.0 23.5 8.5 65.8 72.5 Example 3 Comparative 68.2 65.5 8.87.5 21.4 9.0 69.0 75.8 Example 4

The present invention optimized the viscosity, oligomer content,molecular weight and its distribution, and moisture content of thepolyamide 56 resin. Furthermore, the present invention optimized thespinning process of the polyamide 56 industrial yarn, improved itscrystallinity and orientation degree, increased the setting temperatureand winding overfeed ratio, and reduced the subsequent stressrelaxation. The present invention thus provided a polyamide 56industrial yarn with excellent mechanical properties and dimensionalstability which has a break strength of 8.0 cN/dtex or more; anelongation at break of 26% or less; a dry heat shrinkage and a shrinkagein boiling water of 6% or less; a crystallinity of 70% or more; and anorientation degree of 80% or more.

The foregoing description of the embodiments was provided to facilitatethose skilled in the art to understand and apply the present invention.It will be apparent to those skilled in the art that variousmodifications can be readily made to these embodiments. The genericprinciples described herein can be applied to other embodiments withoutcreative labor. Therefore, the present invention is not limited to theabove-mentioned embodiments. Improvements and modifications made bythose skilled in the art according to the disclosure of the presentinvention without departing from the scope of the present inventionshould all fall within the protection scope of the present invention.

1-25. (canceled)
 26. A polyamide 5X industrial yarn, wherein the contentof copper ions in the polyamide 5X industrial yarn is 10-1,000 ppm, andthe polyamide 5X comprises any one of polyamide 56, polyamide 510,polyamide 512, polyamide 513 or polyamide
 514. 27. The polyamide 5Xindustrial yarn according to claim 26, wherein the content of copperions in the polyamide 5X industrial yarn is 30-500 ppm, or 50-200 ppm.28. The polyamide 5X industrial yarn according to claim 26, wherein: (i)the polyamide 5X industrial yarn has: (a) a heat-resistant breakstrength retention rate of 90% or more after being treated at 180° C.for 4 hrs; and/or a (b) heat-resistant break strength retention rate of90% or more after being treated at 230° C. for 30 mins; and/or (c) thepolyamide 5X industrial yarn has a dry heat shrinkage of 8.0% or less;or (ii) the polyamide 5X industrial yarn has: (a) a heat-resistant breakstrength retention rate of 93% or more after being treated at 180° C.for 4 hrs; and/or (b) a heat-resistant break strength retention rate of92% or more after being treated at 230° C. for 30 mins; and/or (c) thepolyamide 5X industrial yarn has a dry heat shrinkage of 6.0% or less.29. A polyamide 5X industrial yarn, wherein: the polyamide 5X industrialyarn comprises a heat stabilizer, further wherein the heat stabilizercomprises any one of copper acetate, potassium iodide, copper chloride,cuprous iodide, copper oxide, cuprous oxide, or a combination thereof;and the heat stabilizer is added in an amount of 10-2,800 ppm, or100-2,500 ppm, based on the total weight of production raw materials.30. The polyamide 5X industrial yarn according to claim 29, wherein: theheat stabilizer comprises a composition of potassium iodide and copperacetate, and the molar ratio of copper acetate to potassium iodide is1:1-15.
 31. The polyamide 5X industrial yarn according to claim 26,wherein the polyamide 5X industrial yarn has a break strength of: 6.5cN/dtex or more, or 7.0 cN/dtex or more, or 8.0 cN/dtex or more.
 32. Thepolyamide 5X industrial yarn according to claim 26, wherein: theoil-free yarn of the polyamide 5X industrial yarn has a relativeviscosity of 2.7-4.5, and the absolute value of the difference betweenthe relative viscosity of the oil-free yarn and the relative viscosityof its original resin is 0.12 or less.
 33. The polyamide 5X industrialyarn according to claim 32, wherein the absolute value of the differencebetween the relative viscosity of the oil-free yarn of the polyamide 5Xindustrial yarn and the relative viscosity of its original resin is:0.10 or less, or 0.08 or less.
 34. The polyamide 5X industrial yarnaccording to claim 26, wherein: the oil-free yarn of the polyamide 5Xindustrial yarn has an amino content of 20-50 mmol/kg; and the absolutevalue of the difference between the amino content of the oil-free yarnand the amino content of its original resin is 5 or less.
 35. Thepolyamide 5X industrial yarn according to claim 34, wherein the absolutevalue of the difference between the amino content of the oil-free yarnand the amino content of its original resin is: 3 or less, or 2 or less.36. The polyamide 5X industrial yarn according to claim 26, wherein thefilament of the polyamide 5X industrial yarn breaks: 2 times or lessevery 24 hrs, or 1 time or less every 24 hrs, or 0 time every 24 hrs;and the production yield of the polyamide 5X industrial yam is 90% ormore, or 93% or more, or 96% or more.
 37. The polyamide 5X industrialyarn according to claim 26, wherein the polyamide 5X industrial yarn hasa shrinkage in boiling water of: 8.0% or less, or 7.0% or less, or 6.0%or less; and/or the polyamide 5X industrial yarn has a fineness of:100-3,500 dtex, or 200-2,500 dtex, or 300-1,800 dtex; and/or thepolyamide 5X industrial yarn has an elongation at break of 26% or less,or 22% or less; and/or the polyamide 5X industrial yarn has acrystallinity of 70% or more, or 72% or more, or 74% or more; and/or thepolyamide 5X industrial yarn has an orientation degree of 80% or more,or 82% or more, or 84% or more.
 38. The polyamide 5X industrial yamaccording to claim 26, wherein the raw materials for producing thepolyamide 5X industrial yarn at least comprise: 1,5-pentane diamine andadipic acid; or a polyamide 5X obtained by polymerizing 1,5-pentanediamine and adipic acid as monomers; optionally wherein the 1,5-pentanediamine is prepared from bio-based raw materials by a fermentationprocess or an enzymatic conversion process.
 39. A process for producinga polyamide 5X industrial yarn according to claim 26, wherein theprocess comprises the following steps: (1) polymerizing 1,5-pentanediamine and adipic acid to obtain a high-viscosity polyamide 5X melt,conveying the melt to a spinning beam by a melt booster pump, andspinning directly; or by use of chip spinning by initially preparing alow-viscosity polyamide 5X resin, and then obtaining a high-viscositypolyamide 5X resin by solid phase tackifying, and then heating thehigh-viscosity polyamide 5X resin into a molten state so as to form apolyamide 5X melt suitable for spinning; (2) drawing the polyamide 5Xmelt obtained in Step (1) to form an as-spun yarn; and (3) processingthe as-spun yam formed in Step (2) to obtain the polyamide 5X industrialyam; wherein: a heat stabilizer is: added during the polymerization of1,5-pentane diamine and adipic acid in Step (1), or injected online inthe form of a heat stabilizer masterbatch before cutting the polymermelt into pellets, or blended in the form of a heat stabilizermasterbatch during the spinning; the content of copper ions in the heatstabilizer masterbatch is 0.5-10 wt %, or 0.8-5 wt %, or 1.2-3 wt %; theheat stabilizer masterbatch is added in an amount of 0.3-5.0 wt %, or0.5-3.0 wt %, or 0.8-2.0 wt %; and wherein the base material for theheat stabilizer masterbatch comprises: any one of polyamide 6, polyamide56, polyamide 66, polyamide 510, polyamide 610, polybutyleneterephthalate, or a combination thereof, or any of polyamide 6,polyamide 56 and/or polyamide 510, or polyamide 6 and/or polyamide 56;and/or wherein optionally, the process further comprises the step ofadding other additive(s) comprising any one of matting agents, flameretardants, antioxidants, ultraviolet absorbers, infrared absorbers,crystal nucleating agents, fluorescent brighteners and anti-staticagents, or combination thereof; and the other additive(s) are added inan amount of 0.01-5 wt %, based on the total weight of the productionraw materials.
 40. The process according to claim 39, wherein Step (1)comprises the following steps: (1-1) mixing 1,5-pentane diamine, adipicacid and water uniformly under an inert gas or vacuum condition toobtain a polyamide 5X salt solution; wherein the molar ratio of1,5-pentane diamine to adipic acid is (0.95-1.2): 1; (1-2) heating thepolyamide 5X salt solution, increasing the pressure in the reactionsystem to 0.3-2.5 MPa, degassing, maintaining the pressure, thenreducing the pressure in the reaction system to 0-0.2 MPa, andevacuating to a vacuum degree of −(0.01-0.1) MPa (gauge pressure) toobtain a polyamide 5X melt; wherein optionally: the temperature of thereaction system at the end of the pressure-maintenance is 230-275° C.;and/or the temperature of the reaction system at the end of thepressure-reduction is completed is 240-285° C.; and/or the temperatureat the end of evacuation is 265-295° C.
 41. The process according toclaim 39, wherein in Step (1), the low-viscosity polyamide 5X resin in96% sulfuric acid has a relative viscosity of: 2.0-2.7, or 2.2-2.6, or2.4-2.5; and/or the high-viscosity polyamide 5X resin in 96% sulfuricacid has a relative viscosity of: 2.7-4.5, or 3.2-4.0, or 3.4-3.6;and/or the high-viscosity polyamide 5X resin has an oligomer content of:0.2-1.0 wt %, or 0.4-0.6 wt %; and/or the high-viscosity polyamide 5Xresin has a number average molecular weight of: 18,000-40,000, or25,000-30,000, and/or the high-viscosity polyamide 5X resin has amolecular weight distribution of 0.8-1.8, or 1.2-1.5; and/or thehigh-viscosity polyamide 5X resin has a moisture content of: 200-800ppm, or 300-750 ppm, or 350-700 ppm, or 400-600 ppm; and/or thehigh-viscosity polyamide 5X resin has an amino content of: 20-50mmol/kg, or 24-45 mmol/kg, or 28-40 mmol/kg, or 32-36 mmol/kg; and/orwherein optionally, the heating in Step (1) is carried out in a screwextruder, and further optionally the screw extruder includes fiveheating zones; and the temperature of a first zone is 250-290° C., thetemperature of a second zone is 260-300° C., the temperature of a thirdzone is 270-320° C., the temperature of a fourth zone is 280-330° C.,and the temperature of a fifth zone is 280-320° C.
 42. The processaccording to claim 39, wherein Step (2) comprises the following steps:ejecting the polyamide 5X melt through the spinneret plate of thespinning beam to form the as-spun yarn; wherein optionally: thetemperature of the spinning beam is: 270-330° C., or 280-310° C., or290-300° C., or 293-297° C.; and/or the pressure of the spin pack of thespinning beam is: 8-25 MPa, or 12-20 MPa, or 15-18 MPa; and/or thedrawing ratio of the spinneret of the spinneret plate is: 50-400, or70-300, or 80-200, or 90-100.
 43. The process according to claim 39,wherein Step (3) comprises the following steps: thermally insulating,cooling, spin finishing, drawing, and winding the as-spun yam into ashape which comes out of the spinneret orifices to obtain the polyamide5X industrial yarn; wherein optionally, the thermal insulation isperformed with a slow cooling device, wherein the slow coolingtemperature is: 150-280° C., or 200-240° C., and the slow cooling lengthis 10-80 mm, or 20-50 mm; the cooling is performed with quench air,wherein the air speed of the quench air is 0.3-2.0 m/s, or 0.6-1.5 m/s;the air temperature of the quench air is 15-25° C., or 17-23° C., or19-22° C.; and/or the humidity of the quench air is 60-80%, or 65-75%;and/or the winding tension during winding the as-spun yam into a shapeis 50-300 cN, or 80-200 cN, or 100-160 cN, or 120-140 cN; or the windingspeed is 2,000-3,800 m/min, or 2,500-3,500 m/min, or 2,800-3,000 m/min;and/or the winding overfeed ratio is 5% or less, or 4% or less, or 3% orless.
 44. The process according to claim 39, wherein the drawing isperformed in four or more stages; wherein optionally, the drawingprocess comprises: initially feeding the as-spun yarn, which has beenspin finished, to a first pair of hot rollers through a godet roller,and performing a first-stage drawing between the first pair of hotrollers and a second pair of hot rollers; preforming a second-stagedrawing between the second pair of hot rollers and a third pair of hotrollers; performing a third-stage drawing and a first thermal settingbetween the third pair of hot rollers and a fourth pair of hot rollers;and then performing a fourth-stage drawing and a second thermal settingbetween the fourth pair of hot rollers and a fifth pair of hot rollers;further optionally wherein: the total drawing ratio is 4.0-6.0; thetemperature of the first thermal setting is 180-250° C., or 200-240° C.;and/or the temperature of the second thermal setting is 200-240° C., or220-230° C.
 45. A method of using the polyamide 5X industrial yarnaccording to claim 26 in a manufacturing process which produces any oneof the following: sewing threads, tire cords, air bag yarns, releasecloth, krama, canvas, safety belts, ropes, fishing nets, industrialfilter cloth, conveyor belts, parachutes, tents, bags and suitcases.